Hydrogen firing at elevated temperatures to change the color of glasses whose compositions contain reducible ions is well known. A notable commercial application of that technique is found in the Corning Incorporated eyewear product lines marketed under the SERENGETI(copyright) and CPF(copyright) trademarks. The color changes induced are attributed, to the reduction of a portion of the silver and lead ions respectively, in the glass to the atomic state.
Several methods have been suggested for making polaizing glasses. For example, one such method is to redraw a glass above its softening temperature. The glass contains a separate phase which is elongated by the redraw process. The thermal treatment which leads to the phase separation is usually carried out before the redraw process. In a particular version of the above process, the separated phase is initially spectrally non-absorbing material such as AgClBr, CuCIBr, AgI, CuI or copper/cadmium halides, which must be subsequently modified to create a desired dichroic property necessary for the polarizing effect. This is accomplished by treating the stretched glass in hydrogen gas at elevated temperatures for sufficient time to effect the chemical reduction of the spectrally non-absorbing materials to their corresponding metal. The chemical reduction process is a combined process involving both the diffusion of hydrogen in the glass, and the chemical reaction of the hydrogen with the halide phase.
It is known that the chemical reaction proceeds very fast relative to the hydrogen diffusion which leads to the condition of a sharp boundary between the reduced region near the surface, and the unreduced region below the surface. The polarizing behaviors derives from the reduced layer. Also, when the polarizing glass is heated to the vicinity of 500xc2x0 C. for any prolonged period of time, the elongated particles re-spheridize and the polarizing property is lost. That is, the elongated particle returns to its spherical shape. This is explained by the fact that once the glass is soft enough, the interfacial forces act to undo what the redrawing forces had accomplished.
For certain applications, it is desirable to have the polarizing properties restricted to localized regions of the glass. Accordingly, it is the object of the present invention to provide methods of partially or fully blocking the effect of hydrogen reduction over a portion of a glass surface, or other ways of altering the polarizing state.
Briefly, the invention relates to a polarizing glass having an integral non-polarizing region.
In one aspect, the invention relates to a method of producing a polarizing glass in which a region on the glass surface is rendered non-polarizing.
In a particular aspect, the invention relates to a method of forming a glass having integral polarizing and non-polarizing regions by:
(a) providing a glass having an elongated (stretched) reducible phase;
(b) protecting or masking a portion of the glass by selectively forming a layer of material on the surface of said portion of the glass;
(c) subjecting the unprotected regions of the glass to a reducing gas to reduce the reducible phase in said region; and
(d) removing the layer of material from the protected portion to reveal the underlying non-polarizing glass to thereby form a glass having integral polarizing and non-polarizing regions.
In still another aspect, the invention relates to a method of forming a non-polarizing region in a polarizing glass by, providing a polarizing glass comprising reducible elongated phase particles; and then subjecting a region of the glass surface to thermal heating to re-spheridize the elongated phase and thereby render the polarizing glass, non-polarizing in said region.
In yet another aspect, the invention relates to a method of forming a non-polarizing region in a polarizing glass by selectively removing the polarizing layer to render the glass in said region, non-polarizing.
As used herein:
xe2x80x9creducing atmospherexe2x80x9d refers to a gaseous atmosphere in which the chemical potential of oxygen is low. Examples of reducing gases include hydrogen, hydrazine vapor, cracked ammonia, deuterium and forming gas (i.e., a mixture of hydrogen and an inert gas, for example, H2/He and H2/N2).